Awf bin Malik (may Allah be pleased with him) said: I went out with Zayd bin Harithah (may Allah be pleased with him) on the expedition of Mu'tah, and a madadi (a man who had come as reinforcement) from the people of Yemen became my companion; he had nothing with him except his sword. A man from the Muslims slaughtered a camel, and the madadi asked him for a piece of its hide. He gave it to him, and he made it into something like a shield. We went on and met the hosts of the Romans. Among them was a man on a reddish horse, with a gilded saddle and gilded weapons, and the Roman began attacking the Muslims fiercely. The madadi sat in wait for him behind a rock. When the Roman passed by, he hamstrung his horse and it fell; he got on top of him and killed him (the Roman), and took possession of his horse and weapons. When Allah granted victory to the Muslims, Khalid bin al-Walid (may Allah be pleased with him) sent for him and took the salab (the slain man's gear) from him. Awf (may Allah be pleased with him) said: I came and said to Khalid (may Allah be pleased with him): Do you not know that the Messenger of Allah (peace and blessings be upon him) ruled that the salab belongs to the killer? Khalid (may Allah be pleased with him) said: Yes, but I considered it too much. I said: You must return it to him, or I will mention it before the Messenger of Allah (peace and blessings be upon him). Khalid (may Allah be pleased with him) refused to return it. Awf (may Allah be pleased with him) said: We gathered before the Messenger of Allah (peace and blessings be upon him), and I related to him (peace and blessings be upon him) the story of the madadi and what Khalid (may Allah be pleased with him) had done. The Messenger of Allah (peace and blessings be upon him) said: "O Khalid, why did you do this?" Khalid (may Allah be pleased with him) said: O Messenger of Allah (peace and blessings be upon him), I considered it too much. The Messenger of Allah (peace and blessings be upon him) said: "O Khalid, return to him what you took from him." Awf (may Allah be pleased with him) said: I said: There you are, O Khalid! Did I not make good on my word to you? The Messenger of Allah (peace and blessings be upon him) said: "What is the matter?" I told him (peace and blessings be upon him), and the Messenger of Allah (peace and blessings be upon him) became angry and said: "O Khalid, do not return it to him. Will you not leave my commanders alone for my sake? You have the clear part of their affairs, and the murky part of it falls on them."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12783